1. Field of the Invention
The present invention relates generally to backing-up data in a Storage Area Network (SAN) and more particularly to mapping logical files to application host disks in data backup systems.
2. Description of the Background Art
In the prior art a volume is an application host location where a group of one or more files are stored. A file system refers to the structure and arrangements of the files on a computer, a system of computers, or within a portion of a volume. A volume may contain multiple file systems and a file system may span multiple volumes. A file system manager sets up and manages the file system. A volume manager sets up and manages the volumes.
A backup object includes an object identified in a backup class of a program. The backup object may be a tablespace, file, or volume. A backup client is an application on the application host that builds a data map of the objects that comprise the backup data source. The data map associates a file system's logical objects with locations of file or volume data on application host disks. Files and volumes are logical objects managed by file system managers and volume managers.
The data map includes lists of the extent of each storage (to be referred to as storage extents or Storage Extent Descriptors (SEDs)) that identify an absolute disk address, a count of the number of blocks that follow, and a device name. The backup client on the application host then transmits that map to a backup server running on a second host. A block has an address known to the file system by its block number. A block number is the ordinal of the block relative to the start of the file system, which in turn is the start of the volume associated with the file system. This block address is called a volume-relative address because it is computed from the beginning of the volume.
A SAN in a distributed environment often includes numerous computers connected to various storage devices so that any one of the computers can access any one of the disk or tape drives. Such devices include Symmetrix produced by EMC of Hopkinton, Mass.
The SAN leads to a desirable ability to reduce backup overhead on the application host computer by delegating the work of data backup and by reducing manual administrative operations. Commonly, an application host computer delegates to a back up host the task of backing up and storing the data of the application host to the storage devices. In this way, the task of moving data from disk to offline media can be performed without interrupting operations of the application host.
One disadvantage of prior art methods for building maps of logical objects is that such methods are very limited in scope because they are tailored to specific file systems and depend significantly on individual operating systems. For example, a technique arranged between Legato and Hewlett Packard (HP) is highly specific to the HP systems. Further, Legato's original prototype was implemented in the Solaris Unix File System (UFS) and required that Legato have access to the UFS source code. Thus, the prior art does not provide a mapping method that can be used efficiently with different operating systems, file systems and volume managers.
Another disadvantage of prior art backup systems includes the requirement that the backup host access the file system and/or volume manager on the application host during the backup process, thereby slowing down the backup and the application running on the application host.
Therefore what is needed is a system and method that overcomes the disadvantages of the prior art.